With the continuing and growing popularity of minivans and SUVs, removable and flexible rear seating has received increasing attention. It is desirable that rear seats be removable or, in the alternative, capable of being folded and rotated or "tumbled" forward to a stowed position. This allows for extra cargo space when the extra rear seating is not needed, but does not require that the seat be taken out completely. The rear two of the seats four legs can be unhooked from the vehicle floor, and then the whole seat is rotated or "tumbled" forward about pivots on the front two legs. Generally, the seat back is folded down onto the seat cushion into a "table" position before it is stowed. This is a relatively simple process, so long as the seat cushion frame is solid, and not capable of being adjusted fore and aft. Lack of fore/aft positioning has been common for rear seats, but is being added as a feature on newer vehicles, to give rear seat passengers the same convenience of adjusting for leg room. However, attempting to tumble forward a rear seat which happens to also be adjusted to a forward position can present a problem.
As illustrated in simplified form in FIG. 1, a vehicle seat base "B" sits fixed to a vehicle floor "F" in a seating position. A seat cushion frame "C" separate from the base B can be adjusted back and forth on a conventional slide and adjuster, but is shown in its most rearward position. The front legs of the seat base are hooked to F by a pivot assembly, indicated simply by a tumble axis "T.sub.A ". The normal angular position of the back edge of the seat base B relative to axis T.sub.A is indicated by the dotted line "O". The rear of the seat base B can be released to allow the seat base B and cushion frame C to pivot, as one unit, forwardly by an angle .alpha.. The tumble angle can vary between vehicles, and need not be 90 degrees or more in order for the seat to remain up in a stable tumbled position. As shown in FIG. 2, the seat moves to its stowed position with no problem when it is adjusted in its rearwardmost position to start with.
However, as shown in FIG. 3, the seat cushion frame C might have been initially adjusted forwardly by a shorter legged occupant, and left locked in that forward position. In that event, as shown in FIG. 4, it is possible for the forwardly shifted seat cushion frame C to hit the floor F, or possibly the back of the seat in front of it, before it rotates through the entire tumble angle, preventing it from fully reaching the stowed position. Without any compensating return mechanism, the operator would have to return the seat, relock it to the floor, sit in it, adjust it back rearwardly, and begin again.
Providing any mechanism to automatically return the seat cushion frame to its rearward position concurrent with tumbling the seat forward is greatly complicated by the way in which a typical adjuster release works. As illustrated in FIGS. 5 and 6, the most common seat adjuster release is a handle H, pivoted to the seat cushion frame C, which, when lifted against the force of a biasing spring, unlatches the seat cushion frame C from the base B, allowing it to be shifted fore or aft to any desired position, and which pivots back down when released to automatically relatch in the new position. Relative to any fixed point on the seat base B or floor F, the distance by which the handle H must be raised in order to release the adjuster latch varies, depending on where the seat cushion frame C is located. The tumble axis T.sub.A makes a convenient reference frame, since it neither rotates nor shifts back and forth relative to the floor, but other parts of the seat rotate and shift back and forth relative to it. The generally horizontal handle H shifts back and forth past and over the tumble axis as the seat cushion frame C shifts. The handle H, being straight and horizontal, has a least or fixed radial distance Ro from the tumble axis at all adjusted seat positions, but the additional radial distance that the handle H must be pulled up varies depending on the adjusted position of seat cushion frame C. As shown in FIG. 5, when the seat cushion frame C is rearwardmost, the additional radial distance R.sub.g is greatest, because the lever arm is longest. As shown in FIG. 6, the opposite holds when seat cushion frame C is forwardmost, and the release distance R.sub.L is the least, because the lever arm is the smallest. This variation presents no problem to the manual seat operator occupying the seat, since he or she simply pulls the handle H up far enough to unlatch the adjuster, and holds it up while moving the seat back and forth. But a mechanical adjustment means would not move back and forth with the seat cushion the way a human occupant does. Likewise, such an automatic mechanism would have to emulate all the other actions of a seat occupant, including pushing the seat cushion frame C all the way back, and releasing the handle H to relatch. This presents a formidable and complex design challenge.
The only known design that provides a means for shifting the seat cushion frame backward during the forward rotation of the seat base is found in the Renault "Espace" minivan. There, the interference of the seat cushion with the floor of the vehicle referred to above is actually used to unlock the seat adjuster and push the seat cushion frame back. The adjuster release handle is designed to contact the vehicle floor, which contact pushes it up to unlatch the adjuster before the front of the seat cushion hits the floor to be pushed back. This is not a desirable solution for several reasons. Most latch release handle designs would have to be significantly modified in order to extend forwardly far enough to hit the vehicle floor as the seat was rotated forward. This could cause the latch handle to hit the heels of a seat occupant. In addition, not all seat designs will be of a type in which the front of the forwardly adjusted seat cushion hits the vehicle floor. They might contact the back of the seat located in front of them instead, which would not work, since that contact would occur before the latch release handle had contacted the floor. In addition, the latch release handle would remain in the released condition while the seat was stowed, and would not relatch until the seat began to be rotated back to its normal seating position. That would give the seat cushion frame time to slip forwardly again. A far better design would be one that actually prevented contact of the seat cushion or the latch release handle with any other part of the vehicle, and which operated based solely on the normal forward rotation of the seat base.